Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Quando Mika Heinonen e Susanna Dahlberg venceram duplas mistas?
 ###Tabelas: CREATE TABLE past_winners (past_winners_id AUTO_INCREMENT PRIMARY KEY, Year INT, Men's singles VARCHAR, Women's singles VARCHAR, Men's doubles VARCHAR, Women's doubles VARCHAR, Mixed doubles VARCHAR) CREATE TABLE votes_by_state (votes_by_state_id AUTO_INCREMENT PRIMARY KEY, State VARCHAR, Electors INT, Bush INT, Kerry INT, Nader INT, Badnarik INT, Peroutka INT, Cobb INT, Others INT, Margin VARCHAR, Total INT) CREATE TABLE composition_by_molecule_type (composition_by_molecule_type_id AUTO_INCREMENT PRIMARY KEY, Molecule VARCHAR, Percent of Mass VARCHAR, Mol.Weight (daltons) VARCHAR, Molecules VARCHAR, Percent of Molecules VARCHAR) CREATE TABLE first_raiding_cruise (first_raiding_cruise_id AUTO_INCREMENT PRIMARY KEY, Date VARCHAR, Ship Name VARCHAR, Tonnage INT, Ship Type VARCHAR, Location VARCHAR, Disposition of Ship VARCHAR) CREATE TABLE draft_selections (draft_selections_id AUTO_INCREMENT PRIMARY KEY, Round INT, Pick INT, Position VARCHAR, Nationality VARCHAR, School/club team VARCHAR)  
SELECT AVG Year FROM past_winners WHERE Mixed doubles = mika heinonen susanna dahlberg